Q 3: Why does Paul use the terms darkness and light to portray his readers past and future? Before hearing the gospel they lived in the world (darkness) which is full of greed, evil thoughts, selfish desires - Satan's realm. Once they heard and accepted the gospel they were freed from their sin debt, they were filled with the Holy Spirit, and the love of Christ Jesus and the joy of wanting to bear the fruit of this knowledge to all who would listen so that they also would have the opportunity to share in the Kingdom of God and all its riches.
Why does he remind them where they came from? Because Satan is a strong adversary and he will try to pull them back into his realm of darkness
What is the inheritance of the saints in light that he mentions? The Kingdom of the Son he loves and in whom we have redemption and the forgiveness of our sins.
In verse 13 we find two terms used of governing bodies, how are they contrasted in verse 13? The first one is referred to the dominion of darkness from which we are rescued. This is Satan's realm. The second is the Kingdom of the Son he loves in whom we have redemption and the forgiveness of our sins. This is eternal life that we share with God the Father, Jesus Christ his Son, and the Holy Spirit.